90 THE HON. SIR CHARLES ALGERNON PARSONS : EXPERIMENTS ON 



It appears probable that concentration of gaseous pressure causes certain reactions 

 which bring about an association of carbon atoms in the tetrahedral form against 

 their natural tendency to assume the more stable form of graphite.* 



The necessity of subjecting the iron to a temperature above 2000 C. before cooling 

 would seem to imply the necessity of carbides of the other metals, such as silicon, 

 magnesium, &c., being present to insure the necessary chemical reactions with the 

 gases at high pressure within the ingot. 



In reviewing all our experiments, the greatest percentage of diamond occurred 

 when the atmosphere around the crucible consisted of 95 per cent, carbon monoxide 

 and 1 per cent, hydrogen, 2 per cent, hydrocarbons, 2 per cent, nitrogen, the mean 

 pressure in the vessel being about 1 inch absolute of mercury. The weight of 

 diamond we estimated to be about l-f-20,000 of the weight of the iron. If we, for 

 the moment, assume a volume of carbon monoxide at atmospheric pressure equal to 

 0'69 that of the iron, the weight of carbon contained in it equals that of the diamond. 



For the following reasons it would appear that the formation of diamond in rapidly- 

 cooled iron takes place when it is solid or in a plastic condition, or even at a still 

 lower temperature. The rapid pitting of a diamond in highly carburized iron just 

 above its melting point is so pronounced that the largest diamond hitherto produced 

 artificially would be destroyed in a second or two if the iron matrix were molten. 

 The production of diamond was obtained in an ingot rapidly cooled after it had set 

 sufficiently hard to be handled in a spoon. A similar result was obtained in the case 

 of a crucible placed in the die and subjected to 11,200 atmospheres pressure after the 

 contents had set. MOISSAN found the diamonds to occur in the centre of the ingots 

 both in the case of iron and also of silver. 



It lias been seen that iron is permeable to carbon monoxide and hydrogen at 

 temperatures above 600 C., and there appears to be no reason why the concentration 

 of the occluded gases should not take place within the mass as effectively at 

 (500 C. as at higher temperatures, provided that they cannot escape. The most 

 probable temperature, however, may be the point of recalescence at 690 C.t 



It would appear that the function of the impervious metal coating thrown around 

 the ingot by quick cooling might be better effected by gas of the same composition 

 as that which the metal ejects on cooling, the pressure being sufficient to ensure that 

 the gaseous pressure around the ingot shall be equal to, or greater than could occur 

 on quick cooling. Such a substitution might result in a larger gaseous content and a 

 larger proportion of the ingot being brought into a suitable condition for the 

 formation of diamond, and the yield might thereby be increased. Some gradations 



* It also appears that the conditions may operate to the exclusion of some gas or element inimical to 

 the formation of diamond from certain parts of the metal, viz., the graphite liberated and the cooled 

 metal of the outer layers may absorb some gas or element from the inner portion of the ingot and leave 

 none for the central portion. 



t These conditions may also operate to exclude some gases from certain portions of the metal. 



